We investigated the optical and electrical characteristics of Sn-doped indium tin oxide (ITO) thin films. Bi-layer ITO/Sn film samples were prepared by RF sputtering followed by in-situ annealing. Three different conditions with respect to the Sn layer were prepared on a soda-lime substrate: thickness of 0.0 (only glass substrate), 1.0, and 2.0 nm, respectively. ITO films of 170 and 400 nm thickness were deposited on Sn/soda lime glass successively at a substrate temperature of 260 ∘ C. ITO/Sn bi-layer films were in-situ annealed at both 260 and 400 ∘ C for 30 min under 6 × 10 −6 Torr. We studied the optical and electrical properties of the prepared Sn-doped ITO films under various growth conditions, ITO thickness and Sn thickness, and annealing temperature. The best results were obtained from the ITO (400 nm)/Sn (2.0 nm) bi-layer sample annealed at 400 ∘ C, for which average visible transmittance of ~88 % in a wavelength range of 380-780 nm and a sheet resistance R □ of 5.88 Ω were obtained.